But soon after he started work, a man armed with a knife entered the church and slit the throat of the sexton, beheaded an elderly woman, and badly wounded a third woman, according to a police source.
The sexton and the elderly woman died on the spot, the third woman managed to make it out of the church into a nearby cafe, but she died from her wounds, Nice mayor Christian Estrosi told reporters at the scene. None of the victims has so far been named.
What happened in the initial moments of the attack inside the church, a neo-Gothic building in a tree-lined square in the center of Nice, remains unclear.
But testimony from witnesses, mobile phone footage, and accounts from officials, offer an initial if incomplete picture of how the attack ended.
At some point during the attack inside the church, someone ran to a bakery next to the church, and asked staff to call the police.
"I thought it was a joke, I didn't believe it," said one of the staff in the bakery, who spoke to French broadcaster BFMTV and gave his name as David.
But when the person insisted the police should be called, David said he walked the short distance to the corner of Rue d'Italie and Avenue Jean Medecin, where last year local authorities installed an intercom in front of the church that connects directly to the municipal police.
David said he pressed the button on the intercom, and summoned the police. The mayor, Estrosi, who had attended last year's unveiling of the intercom, said this was how police were first alerted to the attack.
David said the police arrived on the scene within 30 seconds, while he went back inside his bakery and pulled down the blinds.
BLOOD AND PANIC
At some point during the attack, the knifeman came out of the church, according to Didier-Olivier Reverdy of police officer's union Alliance Police Nationale.
"When the attacker came out, there was a kind of panic around the concourse" surrounding the church, said Reverdy. "There was blood visible."
Anais Colomna was in the lawyer's office where she works, next to the church, when her phone call was interrupted by the sound of gunfire.
"When I turned around, I saw that they (the police) were firing at someone who was moving away from the church," she told Reuters. The man police were firing at then disappeared from view, she said.
The first shots were fired at 8:58 a.m., according to local officials in Nice.
What happened next is unclear, but it appeared the attacker went back towards the church.
In video footage obtained by Reuters, shot from a balcony across the street from the church, police officers with guns and Tasers raised, could be seen in the side entrance of the church, looking inside. Gunshots could be heard. It was not clear from the footage what they were shooting at.
Estrosi said that, as police were detaining the attacker, "he kept shouting on a loop, 'Allahu Akbar'." The Arabic phrase means God is Greatest. The attacker carried on shouting the phrase even after he was shot and wounded by police, Estrosi said.
The attacker was detained by police at 9:10 a.m., local officials said.
Footage from the same balcony vantage point later showed a man with dark hair on an ambulance gurney being wheeled away from the side of church and into a waiting ambulance. Police with guns surrounded the man on the stretcher, who was motionless.
A witness who observed the scene said the man on the gurney was the knife attacker, but Reuters was unable to independently verify that.
Outside the church a short while later, parishioners gathered to seek news about the victims.
Michele Malé, one of the parishioners, broke down in tears. "We just found out on TV that our sexton was assassinated," she told reporters. "We're in shock."
The sexton -- a lay member of staff responsible for the upkeep of the church -- was in his late 40s or early 50s and had two children, said Gil Florini, a Catholic priest in Nice."He did his job as a sexton very well. He was a very kind person," said Florini.